The Known Worlds comprise the bulk of explored space, defined by The Unity Earth Sphere Alliance. The term was first put forth by Eieber during the Golden Age as a way to describe all that had been explored. Though a clear definition of what constituted the known worlds would not be created in his lifetime, Eieber is credited with the vision to map and establish it.
Types of Worlds
Within the Multi-Verse exist two types of dimensions: Flat and Finite.
Flat words are, quite literally, flat. Large, rocky worlds that are not planets in the traditional sense. Arindell and its famous library are located on one such world. These worlds cannot be reached by space travel, and their ends can often be walked to. Some flat worlds have literal "ends" with cliffs that can be looked over (or infidels thrown over), while others have a repeating horizon. Exploration has proven that although the atmosphere attenuates at higher altitudes, gravity does not; whereas continuance too far from the surface results in collision with an impassible barrier.
Finite dimensions include planets, stars, and even multiple galaxies. They are spherical and divided by membraneous barriers identified as "aether". Ripples within the either form 'reflections' resembling distant starlight/gravity/radio-waves/cosmic radiation, which (accompanied by space-bourne particles, earlier emitted by stars etc.) then bounce back and forth across the whole dimension, creating more and deeper reflections. Through a telescope, this creates the illusion of an infinite or near-infinite universe.
The largest known Finite dimension is called The World.
Essentially a very small finite dimension; may be completely empty or include a handful of stars and planets.
The organizational structure of the Known Worlds is very difficult to visualize or map. Different regions are sorted into 'domains' based on the relative difficultly of getting from one world to another through magic. When the Gudersnipe Foundation introduced the GATE network, transport by magic became increasingly uncommon, the old arrangement of Domains was largely forgotten.
Aether is what separates all dimensions. It is poorly understood by science owing to the inability to observe it directly. Aether is known to be reflective, and have a wrinkled "surface" which reflects and concentrates light. This causes finite dimensions to appear much larger than they are, and creates the illusion of stars on flat worlds.
Division of Real Estate
Geographically by area, Gudersnipe and the Alliance jointly control around 30% of the Known Worlds in an area known as Joint Space, with each side also controlling an additional 10% individually. Thus the two powers comprise over 50% of explored space. Another 25% is comprised of statistically insignificantly-sized governments with no mutual affiliations and not a part of the Alliance or under the protection of Gudersnipe (Read: nobody controls them). M’KHara alone comprises 10%, and the mapped regions of Kamian space represent 5%. The other 15% belongs to the Aten and the Dwarves, though limited interaction between them and humans, coupled with difficulty converting units of measure, has led to a marked lack of understanding in the exact size of the Elven and Dwarven domains. Their lands lie on the outskirts of the Known Worlds and may, if political winds allow for full exploration, eventually double or triple the Known Worlds. It is also important to note that the full scale of Kamian space is unknown, and based on conservative estimates may add an additional 10-20% if and when accurate charting can be performed.
Beyond the Known Worlds
Beyond the Known Worlds lies an uncharted vastness of dimensions, imaginatively identified as ‘The Unknown.’
A statistically insignificant portion of the Unknown has been explored remotely by unmanned GS probes, with manned missions advancing the frontiers constantly. Additionally, numerous Freelancer ships have ventured beyond the fringes of explored space and returned, often with wild tales. Still other ships have never come back; they are presumed missing and probably on a beach somewhere.
Two Worlds Principle
A theory holds that there are only two dimensions: a single, massive finite dimension and a single massive flat dimension. Two different flat dimensions, this theory posits, can be separated by so much distance that one could not possibly cross the area between them.
Arindell is a favored example. Several large continents (including the Greater Continent) have been explored, mapped, and traveled between, but the distance from one end of this region to another is many tens of thousands of miles. People can, and have, spent a lifetime traveling across just the Greater Continent. While many flat worlds have known edges, the edge of Arindell has never been found. If the entire dimension had a diameter of just sixteen light-seconds (the average orbit of a habitable planet around a main-sequence star), the surface area would be nearly seven trillion square miles. The diameter alone would be nearly three million miles. If all explored and mapped flat dimensions were combined, the total area would be less than 10% of the sixteen light-second diameter circle. It is therefore supposed that Arindell is merely the convergence-point at which all the flat dimensions co-incide.
While this theory is largely discounted, at least for the modern world, it potentially holds true for the Mythical Age.